In the movement of air through ductwork in air conditioning systems, it is frequently necessary to determine air velocity at a given point. Velocity sensors such as pitot tubes are used. These sensors require a relatively uniform, or predictable, cross-sectional flow, at the location in the ductwork where velocity determination is being made.
When it is necessary to place bends, such as elbows, or turns, in the ductwork, turbulence is created. In passing through the bend, the air is packed toward the outside of the bend, resulting in non-uniform, cross-sectional flow as the air, with turbulence, exits from the bend. The air flow downstream of the bend then takes some time and distance to return to a relatively uniform, or predictable, cross-sectional flow.
In many instances, it is highly desirable to sense flow close to the bend on the downstream side. For instance, where terminal or mixing boxes are used to selectively mix hot and cool air, and to control flow from a box into a room, it is necessary to sense flow into the box. When turns or bends in the ductwork exist close to the box on the upstream side, as is most frequently the case, a problem occurs, since the bends create turbulence in air flow between the bend and the box, and this prevents accurate flow sensing.
The present invention is concerned with producing uniform, or predictable, cross-sectional air flow in a duct relatively close to a bend or turn on the downstream side to permit accurate air flow sensing.